The invention relates to a device for switching on a drive train in a motor vehicle with a power divider for several drive trains. At least one of the drive trains is permanently coupled with a drive unit and at least one drive train can be connected to the drive train unit, one or more of the drive axles and the drive unit. The invention includes an input shaft and an output shaft which can be connected to the input shaft through a coupling in the form of an axially actuated friction clutch.
Devices of this sort are provided in motor vehicles which, under normal conditions, are driven by only the axle or axles of the first drive train. When insufficient traction is on that axle, the axle of the second drive train can be externally switched on. Actuation of the friction clutch can be effected hydraulically, electro-magnetically or electrically.
DE 39 08 478 describes an electrically actuated device which has the disadvantage of having an electric motor with a complex special construction for the purpose of power conversion where the ball pinion arrangement is located within the rotor of the electric motor. Disengagement of these members would expand the axial unit space of the device.
U.S. Pat. No. 4,895,236 discloses an electrically actuated device with a ball pinion arrangement whose rotatably driven member axially shifts to actuate coupling. The rotation drive results through an electric motor situated outside of the housing. For this reason, axial shifting in the rotation drive gear registers high frictional powers. Thus, the hysteresis of the shifting device is disadvantageously high.
The object of the present invention is to provide a device which can be simply and inexpensively actuated, which functions with low friction, and can be easily included in electric motor and motor vehicle control systems.
The solution therefore exists in that, for regular actuation of the frictional clutch, two rings rotatable through 180.degree. of each other are provided in coaxial arrangement to the clutch disks. One of the rings is a rotatable support ring axially supported in a housing. The other ring is a pressure ring which can slide axially on one of the shafts. A circumferential means bears against each ring on paths in the rings which can be varied axially around the ring periphery. The drive of such an actuating unit, which can be propelled by a suitable electric motor, is installed within and externally of the housing. The drive is completely uncomplicated and enables fine control and regular torque distribution between both drive trains, especially in the absence of a mixing differential. The adjustable motor can be externally attached to the housing by flanges. In an advantageous improvement, a portion of the housing can protectively surround the adjustable motor, so that special protection is offered by its complete incorporation in the housing, including protection against dust and moisture.
A first embodiment consists of a cylindrical chamber on the transmission housing which an ordinary electric motor may be fit.
According to a second embodiment, a standard production electric motor, without a motor housing, is supplied directly in a cylindrical chamber on the transmission housing and covered with a lid.
In each case, arrangement of the adjustable motor is preferably with its rotational axis parallel to the driveshaft so that the drive of the shift device can result through a simple spur gear reduction gear. The electrically actuated shifting comes in combination with other aforementioned electrical control systems for motor vehicle engine performance. Such systems are wheel suspension and steering influence which are intended for the new trends in motor vehicles, reticulation network and, as the case may be, a common specification. The shift is extraordinarily friction poor. The frictional powers in the shift drive could be additionally lessened, so that the adjustable motor is effected by pulsating voltage. In the effect of coupling with friction contact, the adjustable motor remains electrically effected in the preferred arrangement while release of the clutch causes a reversal of electricity.
The ring paths are ball grooves with opposing orientation of varying depth from each other around the ring periphery. The balls travel in paths and preferably are bound in a cage element. Additionally, a varying radius can be provided to vary the depths of the grooves, which radius can influence the characteristic of the torsional angle.
According to another simpler construction, ramps can be formed on one of the rings, on which a cam can be slid on the other respective ring. Also, ramps with bevel rollers situated between the cage element can be provided.
In a preferred embodiment, the clutch is built into a common housing with the power divider of the motor vehicle. The input shaft and a constantly driven output shaft are coaxial and rotatably bound with each other. The engageable output shaft is parallel to the input and connected output shaft. The clutch can be situated coaxially with the input shaft or to the engageable output shaft. In the first case, the output side of the clutch is a mounted sleeve which is rotatably mounted across the drive shaft, and is engageable with the output shaft. In the second case, the input shaft of the clutch can be a rotatably mounted sleeve across the engageable output shaft, which is in torsional engagement with the input shaft.
The drive connection of the input shaft to the engageable output shaft can be effected through a spur gear drive, especially with an intermediate wheel, or through a chain drive.
Preferably the shaft of the adjustable motor lies through a plane essentially parallel to the mounted shafts. If the adjustable motor and the clutch lie across each other on sides of the spur gear drive, or respectively of the chain drive, the transmission shaft of the shifting device can be journaled through the catenary or through a hollow wheel of the spur gear. However, the adjustable motor and clutch could lie on the same side of the spur gear drive, or respectively, the chain drive, thus simplifying the construction of the shifting device.
According to another embodiment, the clutch is situated behind a power divider while switching on the drive train, and attached to the power divider through a shaft drive train. The clutch can thus be built in with the differential drive, especially in a common housing with the axle drive.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.